1. Field of the Invention
The present invention relates to an apparatus and a method for continuously granulating powder material, in particular to an apparatus and a method for granulating powder material used in the food processing field.
2. Description of the Related Art
In the food processing field, there is known a continuous granulation method such as an agitating granulation method, a tumbling granulation method, a continuous vibration fluidized bed method and the like, and a batchwise fluidized bed granulation method, for granulating powder material.
The continuous vibration fluidized bed method is disclosed in Japanese Patent Laid-Open No. 62-247833. In this method, powder material is continuously dropped to form a uniform powder layer having a predetermined thickness. Pressured mist water is then added to the upper surface of the powder layer and thereafter the powder material is forced to move by a vibration mechanism and thus granulated.
However, the conventional continuous granulation method forms for example a high density powder layer of the material, and the granules of the material become hard. Therefore, it has been difficult to obtain the granules which are porous and have a good instant characteristic by the above-mentioned conventional continuous granulation method. A good instant characteristic means that the granules are easy to disperse and to solve when adding boiled water thereto.
The granules having a good instant characteristic can be obtained by the conventional batchwise fluidized bed granulation method. However, since the batchwise fluidized bed granulation method employs a batch operation, the batchwise fluidized bed granulation method needs labors of a relatively high numbers and therefore the labor productivity is low.
Further, in the conventional method disclosed in the above Japanese patent, it is difficult to obtain granules having a good instant characteristic, since the granules are hard, and thus use of the vibration mechanism for moving the powder layer by force is necessary.